best available copv



Sept. 10, 1929. E. E. WlNKLEY ODOGRAPH Filed June 27, 1924 9Sheets-Sheet Qmvew/io 7 a 7 1; 'fi 5 p 1929- E. E. WINKLEY ODOGRAPHFiled June 27, 1924 9 Sheets-Sheet 2 Mlli/vew l'a 7' Sept. 10, 1929. E.E. WINKLEY ODOGRAPH Filed June 27, 1924 9 Sheets-Sheet 4 Sept- 0, 192 E.E. WINKLEY ODOGRAPH 9 Sheets-Sheet 5 Filed June 27, 1924 p 0, 1929. E.E. WINKLEY 1,727,460

ODOGRAPH File June 1924 9 Sheets-Sheet 6 Sept. 10, 1929. E. E. WINKLEYODOGRAPH Filed June 27, 1924 9 Sheets-Sheet '7 tar /gzvew Sept. 10,1929. E. E. WINKLEY ODOGRAPH Filed June 27, 1924 9 SheetsSheet 9 Evevzta 7 M 67/ Patented Sept. 10, 1929.

harem oFricE.

I ERA si'lUs is. WINQKLEY, OFLYNNQ MASsACHU SETTS.

' 5 TlApplieation filed June 27,

- This invention irelates to; anj instrument for recording, in true formand proportionat'e scale,ithe path 'traveled by anyfvehicle in which itmay be installed. :Because the instrument inv-' its=pr'e.ferred form'draws: or marks thepath'on' a record 's'heet, it; has been named anodograph -fro1n-the Greek odo, the "Way iorr pzith, and" :graph, to drawor mark.- -i 1t' 1, While the instrument is'susceptible of various uses,both on land and sea. it is particularly useful in plotting the paths ofland vehicles which," of necessity, are forced to travel'ofl of highwaysandroads and at times in darkness, for' 'exa mple the' tan-ks employedfor oifense in military operations. For brevity of descripti'on,=;"-andwithout limitation on the scope of its us'es, the'iodograph 'willhereinafter be described as performing its functions in an Army tank.

"In time 6f war 'allfroads leading to the front are heavily congestedand if, infpreparingfor an ofl'en'si-ve, or'in bringing upreinforcements, tanks" going to the front were permitted to use theroads, their'slow movement would cause serious blocks'and, by thusaddingtb the many difficulties-to be overcome in =any;event,1nightcause'a failure of the plans" of the commander and jeopardize thelivesof 'many-troops, Ac cordingly it has been the custom for tanks toproceed toward the ,frontacross country, at night when near the;frontffindi'ng' their obijlective asibest they may by inquiry and ot eravailable means. Same times a road Will be crossed during [such travel,but since the troops that maybejmoving on that road generally do notknon where the road"- leads or, if theydo, whatpart uofjthe' road theyare on, much time is l ost by the tank commander in locating hisposition before he can proceed. Ottentimes the objectivefis not located.and when daylight comes the commander may find his tank withinftheenemyslines.-f v f Furthermore, 'with the development of radiocommunication',v"it isxpo'ssible for the tank commander to keep hissuperior offi- 'cer, at therear, informed of his location, if he candetermine such location himself. It

| 1924, Serial N0; 722,673.

is highly important after an offensive for headquarters to know, withcertainty, what point the tanks'have reached so that supporting troopsforflconsolidating the posi tion,won-may quickly be sent forward. It iswell-known thatin the early days of the use o f;tanks in the'VVorld Warhard'won positions had to be abandoned because the commanders of thesupporting troops could not bringithemselves to believe that the tankshad-actually reached the point which-the message insisted had beenreached. Serious and-costly mistakes of this'sort would havebeenleliminated if the tanks had been equipped with some mechanism ordevice, in which headquartershad confidence, for correctly determiningtheir *exact position on the tcrrain'over which they were sent.

One object of the present invention is to provide'an. instrument forinstallation in all moving vehicles Where it may be useful, that may beused,'in conjunction'with a map of the terrain being t'raversed' orchart of the sea being sailed, to indicate or show at all times duringthe operation of the instrument the location of the vehicle on the mapor chart, provided that the starting point and a directional baselineare first correctly determined. The employment of such an instrument inany movable land vehicle, or ship, will enable the position of suchvehicle to be indicated so that its location and direction of-travel canbe known and registered even though travelling in a smokesc re en, fogor darkness. A 'further object of the invention is to provide aninstrument which upon installation in a moving vehicle will, on drivingthe vehicle over a plot of country, reproduce a map of the coursetravelled, which may be completed by indicating thereon contours andother details of the terrain. Such a use of the instrument is valuable,for example, in making surveys or in plotting routes for travellers bymotor car or otherwise.

Accordingly the invention is featured by a map carrier (it beingunderstood that a blank sheet of paper is included in theterm "map)having a scriber or style cooperating therewith for recording thelocation of the vehicle on the map; means for causing a relativemovement between the scriber and map in accordance with the travel ofthe vehicle; means which keeps a timed speed relation between thevehicle and the feed and preferably allows the feed to be operative only'at predetermined intervals; means which governs the length of feed, andconsequently the scribing on the map, according to whether the-vehicleis travelling on relation "between-the rate of sp eedof the vehicle hnd'themefriodic movementsof a feed poi nt which operates to move the druma redetermined distance, i. e. one traveL unit, at each cycle or feed,and an inelinometer which governs the length of "feed to-the extent-that'the delineation by the scriber on the map is in correct linear, "orhorizontal; distancesmegardlessof :the hills andvalleysthatsniaylbe'traversed by the vehicle in travelling'therouterecorded. 'Io the 'acconiplihmentwof these objects and such others'asmay hereina fter appear, as will readily be recognized by those skilledin the art'fromirthe following description, the invention comprisesfeatures and "combinationsrof parts heifeinafteridescr-ibed and thenparticularly-pointed out in the ap- P nded-claimsix 4 i I 4 Th"eprefer-red frm.zof the invention is illustrated in the accompanying"drawings in which: I

Figure 1 is a view, in front elevation, of the entire instrument;

Fig. 2 isIau-sectional plan view, on the line 2--2 of Fig. 3 withtheycasings at the two ends of the frame omitted; I

' Eigx3is a w'iew, in side ;'elevation,='of*the rightshand orfgearbox-end, of the instru ment showing the map-drum brake-mechani'sm indotted lines;

Fig. 4 is' -.a detailview, in side elevation, of thecams and relatedmechanism at the lefthand end of the instrument for operating thefeed-point under control of the inclinometer; Fig.4 is adetailfiliustrating. the relation of certain parts oft-he feedcontrolling meclr anism at the-end ofla feed stroke;

r Fig. 5 is a view,--in side elevation, of the cam andv relatedmechanism at the righthand end of the instrument for impartingventical-movementof the feed point;

Fig. 6 is a detail view, in vertical section,

slide block a movement of which actuates the sticker point to feed themap;

Fig. 12 is-a' view, in side elevation, of the pendulum chamber of theinclinometer shownpartlyin section to illustrate interior details; 1"

Fig. 13 is a view, in vertical section, of the inclinometer;

Fig. 14 is a view, in' elevation, 'ofithe feeler cam chamber of theinclinometer with the outside cover plate removed; :2 a 15'is a view ofthe mechanism Within the gear box at the right-hand-endof theinstrument, the parts being shown asfthey appear "on the vertical plane1515 of Fig. 16; v

Fig. 16 is a view, in side elevation, of the mechanism shown in Fig.15-taken on a line 16-16 of said figure; I Fig. 17 indicates a large mapof country over-which; military operations are being conducted and themanner of obtaining the smaller map showing the particular sector to beused on the drum of the odograph and containingthe starting pointandobjective to be reached; F-ig.'=18 is a diagrammatic plan development of-the-map-drum having a map in place thereon, land the dial forsynchronizinguthe direction 0% the path of the feed-point ,with thevariation of north onthe map from the gyroscopic base linewhich isillustrated as true north. In this figure the direction-of the path ofmovement of the feed-point, in its calibrated position, is shown by anarrow, formed bydashes, on the movable scale;

Fig. 19 is a view, in elevation and partly in section, looking intotheend of the gear box on the plane of line l919 of Fig. 20,

and illustrating the intermittent. mechanism controlling-the feed; and 1I Fig. .20 isa view, in elevation, of the mechanism shown in Fig. 19,taken'on the confined to a use of the instrument in an Army tank, but itshould distinctly be understood that such mode of presenting theinvention is for convenience only, and is in no manner a limitation uponthe scope'of the invention which, as heretofore stated, may successfullybe used in other environments and for various purposes. I

The different elements of the instrument are supported on a generallyU-shaped frame comprising a base 6, normally held parallel to the baseplate 2by the springs 4, and right and left sides 8 and 10. The sidesare connected, substantially midway their height, by a horizontalcross-web 12, and further braced by two vertical skeleton crosswebs one,14, at the rear andanother, 16, arranged centrally. p T

Before describing 'the vario'u's mechanisms inj detail the principalelements of the instrument and their relationto eachother,willbe"des'cribed briefly; A;"map-drum 20 is supportedabove the framefor free rotationalandsliding movement on a shaft 22 the endsof'which'are held between two upright wing-brackets 24 and 26extending-lab erally fromthe side plates 8 and 10 respectively (Figs 1and 3); A scriber 30, which may be a pencil, is carried bya'pring-pressed holder 32 supported on a transverse shaft 34 infront ofand parallel' to the map-drum axis."the ends of which are journaled intwo head-brackets36 and"38',(Figs. land-3) extending forwardly andupwardly fronithe side plates 8 and 10 respectively being boltedthereto,"as best shown by Fig. '3. Thus a rotarv, a sliding. or acombined rotary an'd sliding'movement of the drum20 on its shaft 22 willcause the scriber to, mark a path' on the map that is parallel.perdendicular or oblique, respectively, to the map-axis i. ,e. 'a'central circumferential line the plane'of whichis normal to the axis ofthe map-drum,

Beneath the map-drum" 20, and in the vertical plane of its axis, is thefeed-point 40' (Figs. 2 and 6) which periodically engages the map on thedrum'and movesthe drum in such a manner as to cause the scriberto makesuch a 'mark on the map, in direction and extent, as will alwayscorrectlv locate the position of the tank on the terrain bein traversed.The feed-point is always advanced to a predetermined position but'theangle of its path of movement relative to the mapaxis, hereinbeforedefined, may be variedfor a purpose later to be'explaine'd." Whateversaid relative direction of the feed may be, its fixed relation to thecompass-bearing-is maintained, regardless of'variations in the directionof travel of the tank. This is-accomplished by mounting the feed-pointon a supporting structure, indicated generaL ly by 42 in Fig; 6,comprising an angularly adjustable vertical shaft 44 (Fig. 10) seated ina lower bushing that is bored axially to receive and hold the upperprecession-ring pintle 46 of a gyroscope 50. The upper pintle 46 isjournaled in the cross-web 12 (F ig. 6) and the opposite lower pintle 48is similarly journaled in the .frame base 6, thus supporting thesteering element in the lower part of the frame between the side plates8 and 10. The base is provided with a ledge 3 (Figs. 1 and 3) forsecuring in place a casing (not shown) having a sight window that may beopened tor-place'a map or remove it from thedrum 20. I

3 Theinstrument preferably is so mounted that it stands vertically, asshown in Figs. 1 and 3, since a vertical position makes inspection ofthe' map more simple, but those skilled in the art will recognize thatthe -instrumentis so'designed that it may be adjusted for effective andperfect operation in positions other than vertical. The scriber 32 isfixed centrally on its shaft 34, and, therefore, remains in the fore andaft vertical plane passing through the axes of the precession-ringpintles. The teed-point 40 as will presently appear, while mounteddirectly below the scriber may have its path of movement in said foreand aft plane or at any angle to it. according to the relation of thedirection in which the tank is travelling to the constant directionof-said path as maintained by the steering element, The gyroscope 50 isof a type permitting the axis of its rotor to be turned at anyangle tothe true north that may be found convenient or desirable andthis'position will then 'be maintained while the rotor is in operation.This is important, in the use'of the odograph within a tanlc'because'ofthe diflic'ulty of obtaining outside sights by which, the rotor shaftmay be laid true .north and south. Means is provided on the feed-point.shaft 44 for calibrating thev'initial heading of the tank to the angleof'the rotor, shaft. whatever it may be. v

All distances on the map are linear. or horizontal distances and hence.for a correct record of the path oi travel. the ratio of the rate offeed to the scal of the map must he rectified when the tank istravelling uphill or doivn-hill, the feed step being increasinglvshortened as the obliquity of the gradient increases. Accordingly thefeed mechanism is controlled by an inclinomcter (Figs. 12-14) containedwithin a casing 52 secured to the left-hand side frame 10 (see Fig. 1)and comprising a movable feelcr 54, the upper end of which is connectedto mechanism for controlling rectifications of the length of the feedstep, and the lower end of which. at times, engages a pendulumcontrolled inclinomcter cam havingtwo surfaces 56 and 58 for unhill anddownhill rectifications respectively.

The length of each periodic feed step of the feed-point 40 must beregulated to ,accord with the scale of the man upon the drum 20 Power todrive the feed mechanism of the odograph may conveniently be taken fromthe transmission gear and transmitted through a flexible shaft 62 (Fig.3) to the feed-cam shaft. Conveniently, although not necessarily, atrain of reduction gearing is used, indicated generally by 64 (Figs. 15and 16), which 1 connects with mechanism 66 for driving the cam shaftfrom either a right or left drive from the transmission, all of which isenclosed within a gear box 70 secured to the right hand'side frame 8(see-Fig. 1).

Having thus indicated generally the principal part-so-f the instrumentand the manner in which they co-o'perate to cause'th'e scriber to markthe' path traversed by the vehicle, in which the instrument isinstalled, on a map bound onthe map-drum, a detailed description of thevarious mechanisms will now be given. 1 .f .7 The preferred type 0fgyroscope for. use. in the odograph is one that is perfectly balancedand provided with three degrees of freedom. It comprises 'a rotor.preferably electrically driven, mounted or rotation within the casing72-Whi'ch is journaled at 74 and 76 forhorizont'al oscillation vithinthe periphery of the outer housing or precession-ring 78, Theprecession-ring. in the present instance, is vertically sustained bysuitable, self-aligning hearings disposed at substantially right anglesto the casing journals. The housing .78 l'S-PI'OVidEd with an adjustableweight 79 (Fig. 1) to balance the whole element against precessingas theresult of varying rotational forces of the earth at different latitudes.Y

It is obvious to those skilled in the art that since a properly balancedgyroscope maintains its position in azimuth as the result. of certainactions and reactions, itis within the scope of the invention toemp1oy,,any other means that would indicate a fixed or base line, byresponding to similar or even difi'e1"- ent forces such as vibrations ofheat, light, or electricity in its various manifestations. In itsbroader aspects the invention may be defined as the combination ofcertain forces, which will be called the directional vconstunt, withmechanism designed to produce in commercial form a reasonably correctrecord of a route or course travelled. From the foregoing it will beunderstood that the gyroscope is merely the preferred type ofdirectional constant and that this term, and such terms as steering groscope, and steering element, are. in the present case, synonymous andbroadly inclusive.

Electrical current for driving the rotor of the steering gyroscope 5Qenters and departs through the binding posts 80 and 82 (Figs, 1 and 3)respectively, the circuit through the gyroscope being in accordance withcommercial practice and well known. Mounted on the upper pintle 46,between the precession or gyro-ring 78 and cross veb 12, is a disk 84(Figs. 1 and 6), and extending downward through the web is a stud withina housing 86 having a knurled head and having its lower end slabbed offfor engaging the edge of the disk 84. When the parts are so engaged thegyroscope is-locked from movement. Disengagement iseffected by liftingthe stud against the force of a coiled spring within the housing andrestinga radially .26 provide cone bearings which frictionally,

hold the shaft from rotation by reason' of endwise premure from- ;aspringv pressed bunter 90 on the:bracket .2 1"(Figs. 1' and 3). Thebunter .is. pivoted at -92 and aspringpressed plunger 9 1, housed in thebracket, bears beneath a lug on the .bunter and holds it in position forsupporting the shaft A finger-hold 96 permits thebunter to be withdrawnand the map-drum to be removed fronr-t-lie instrument. -The map, afterhaving been prepared ashereinafter described, is wound about thecircumferential surface of the drum a'nditsends are clamped in an axialslot by means of a filling bar 98 which is firmly held in place bypositioning the wire bails 100, pivotally mounted on the spiders88,over. end shoulders-on the bar. The scriber-holder 32 is secured by aset-screw (Fig. 1)- at the desired angle on the shaft 34 which isprovided at one end with' acrank arm 102. A. tension spring 104 has 'itsends attached to a pin on the crank arm anda-pin on the bracket 36, thearrangement beingsuch that the scriber 30 is held yieldingly against themap on the drum 20 (see Fig.

The feed-point 40 is mounted atthe center of the inner ring 106 of acommon gimbalringconstruction (seeFig. 6),'the outer ring 108 beingsupported by bearings in the form of points 110 carried by a U-shapedframe 112 (Fig. 2) provided with rear bushings 114 slidable upon twoupright posts 116 and 118 the ends of which are fixed in upper and lowersleeves at the rear edge of the cross-web 12. The feed-point holder 120is of the form shown in Figs. 6 and 11 having a threaded socket toreceive the point, a tail 122 and an intermediate, smooth-sided block124. The purpose of threading the feedpoint 40 into the socket formedfor its reception in the head of the feed-point holder 120 is to permitan adjustment of the feed-point relative to its axis of oscillation onthe bearings 110 of the gimbal-ring, and thus to vary the length of thefeed-step to accord with any given conditions. The block is receivedwithin the forked, upper end 126 of the vertical shaft 44, and the taildepends in a vertical slot formed at the forward end of a horizontallymovable, cylindrical feedslide 128 seated in a bore at the lower endof'the fork 126. The'tail is pressed against the forward face of apartition 130 in said slot, by afla-t spring 132 secured in an axialgroove in the shaft 44, and bearing against the rear face of saidpartition is the vertical hook 134 of a feed arm for actuating thefeed-point 40. The feed-arm is in the form of yoke 136, encircling asquared portion 137' of the shaft 44 (see Fig. 8), which car- .riesa.vforward, horizontal hook 138. -A

short horizontal pin 140 is secured by a set screw in the squaredportion 137 and the yoke armsare journaled on its pro ecting ends forrocking movement thereon. In

Fig. 6 the feed-point is shown in position to begin its advance and itwill be observed that any movement of the feed hook 134 to the left isimmediately effective to tip the gimbal-ring and effect the feed. Forthe present it will be understood that the position of the .feed hookmay be maintained by a pair of shoulders 139 on the shaft 44 againstwhich thearms of the yoke 136 are held-by the flat spring 132. Withoutgoing into the detail of the construction at this time, it will beunderstood that the shaft 44, while angularlyadjustable as hereinafterexplained, is in fixed vertical position by being clamped at its lowerend within a central bore of the stand 142, forming the main supportingelement of the feed-point supporting structure indicated generally byThe stand 142 is secured at its lower end to the upper gyro-ring pintle46 by means of a set screw 143 (see Fig. 6).

The feed'point 40 has a quadrangular fourmotion path; first, up, whilestanding at an angle to the vertical as shown in Fig. 6; second, to therear, about the gimbal-ring I pivots as a center, until its axis is invertical alignment with the vertical gyro-axis; third, down, and movingat this time in a path in extension of the vertical gyr'oaxis; andfourth, angularly forward, to its initial position as illustrated. Itwill be understood that it is within the scope of the invention to varythe quadrangular motion of the feed-point from that just described, forexample the feed-point mayadvant-ageously enter the map while movingradially toward the drum and end its feed in an oblique position. Beforedescribing the means for tipping the yoke 136 in a direction to advancethe feed-point, the means will be described for raisin the feed point'topierce the map and then lowering it after the feed has beencompleted,sinoe the construction of the feed-point support, justdescribed, has a direct relation to this vertical travel of;thefeed-point. J ournaled in-the side plates, at the rear of .the posts116. and.118, is a. transverse cam-shaft 150. which passes; through theside plate 8 and projects-into :the gear box 7 0. The intermediatemechanismi be tween the flexible driving shafti62z and the cam shaft l50will. bei'described'ini detail later, it being of moment now only toknow that the cam shaft is timed to impart: a feedstep to theifeed-point-40 atepredetermined intervals in accordance with the ratioof the length of feed .step to the-scale of the map on the drum. At theright of the cam shaft (Figs. 2 and 5) is'found a camsdisk1-52, havingat its inner face a cam-path 154 forl'raising and loweringthewfe'ed-point'which will be called, for convenience the iliftinglcamlA'short shaft 156 is fixed: at its-'endspin" the side plate 8 and aninterioribearing 158,- in position above and to the rear' of' thel-camshaft. .Journaled on thefixed -shaft =156 is a bell-crank 160 having avertical-arm carrying a roll 162,-engaged by the lifting cam and ahorizontal arm. pivoted;at.164;;by-its forward end to the upper end ofan adjustable link 166, the lower en'dof Which in turn, pivotedat;.168'.to;thelower bearing sleeve of a yoke member 170depending fromthe frame. l12i whidhsupports thegimbalring. The link 166 is providedwith a%turnbuckle by meansiofzwhicli' the. "linkmay: be made longerorshorter 'as inlay required to compensate forithevertical position-ofthefeed-point within Ethe h'olderniThen lower bearing sleeve of the yokelslides on the post 116 (see Fig. 2). The -lifting cam,raises and lowersthe frame 112 on the. upright posts and consequently =t-he gimbal-ringand its feed-point 40. .The :-block 5124 of-the feed-point holderslides,at. such! times, within the forked end -126':'of shaft44i (Fig. 6) andthe partition 130.0f feed-slide'il28 is so proportioned that contact iofthe tail 122 therewith is never lost. 1'

The feed stroke of thelfeed point 40 may convenientlybe:;'fixed.atoabout one thirtysecond ofan inch, this equalling, ontheusual scale of war maps, a,unit-=of. measure of fifty-five feetlinear distance on the map; The unit of measure is, obvious1y,"a matterof choice. The means by which the gimbalring is tipped aboutits bearings110 in the frame 1,12-to swing .the feed-point-through onethirty-seoondof an inch are :willnow be described. Any movement to theleft, in Fig. 6, of the feed hook 134 will cause the feed-point holderto tilt within the fork 126, and when the pressure is relieved thespring 132 will return the feed-pointwto its starting point i. e. totheposition illustrated .in'Figs. 4ia-nd26. The' hook 134 is'actuated tomake a feed stroke-by tilting the feed arm 136- on its pivotMO throughpressure on the'forward hook 138. To this end the cam shaft-is providedwith a cam disk 172 adjacent the side plate (see Fig. 2), having-at itsinner face a cam path 174. which will be called, for convenience, thefeed cam. .:A short shaft 176 is fixed at its ends in the-side plate 10and an interior bearing 178 (Fig.2), in position above and to the rear?of:the camshaft. Journaled on the fixed-.shaftl? 6 is a bell-crankhaving a .vertical'arm 180 :and a horizontal arm 182 (Fig. 4).= 'Pivotedto the .forward end of the arm 182 is a'link 181 whichdepends and ispivoted also at 186m 'a-long sleeve*188 mounted toaslideon' the verticalpost 118.. This sleeve 188.1is;also shown in- F igs.- 6 -and 8 auditcarries 'an.-annulus:190 having a crosssection (see' Fig.i-6)- whichprovides a shelf. or shoulder? above the forwardxhookll38 of the feedarm 136 sothat on depressing the ring 190 the feed :hook-134is moved ina direction to effect a feed stroke of the feed-point 10. The. purposeofzina'king this actuator in the formof-aring will appear later. The-ring 190.is steadied inits vertical movement by having a bearingformedby a sleeve 192, on the vertical post-1116. ,The. ring 190 is heldin a .position o'flelearance above the forward hook 138-ofthex1feed arm:(see Fig. 6) :by a coiled springzl9lconnected at one end to the uppercross beam-which supports the ver ticali-posts and at.itsother to thelong bearingssleeve 188; The amount ofthis-clearanee is. determined ubya-astop screw 193, threadedgthrough 'said cross beam, ainst the-lowerend-of whichthe lever 182 is held by the spring 191. -'=;The importanceof maintaining this-clearance will appear later. 1 ":;The feed oam:174is so designed that if the'vertical :arin 180 ofthe bell-crank wereprovided-:with a rollto be engaged by the cam,v the actuator. .ring 190would periodically be depressed after each upward movement of thefeedO'int-AO due -to'the operation 'ofthelifting cam 154, and the full throwof the cam would be transmitted to the. feed-point after it had engagedthe map. Since .distances on the mapare horizontal or linear distancesit'is requisite, in order. topreserve-the true relation of the pathmarked on'the map-to the actual position of the tank on the-terraintraversed toshorten the feed step when the tank is travelling up-hill ordown-hill, the length being proportionately reduced according to thedegree of the grade. =Mechanism is therefore provided, 'co-operatingwith the bell-craiik arm '180,--to impart to it a slight movement, priorto the engagement of the map by "the feed-point,- proportionate to thedegree'thatthe odograph is tilted from thenvertical whengthe floor-of--the tank in wfhidiithe odograph is installed' ass'umes anobliqueposition due to traversing .a gradient. This advances thestarting position of the feed-point,- to a varying degree, but does notalter'thepoint at which each stroke finishes. Such compensatingmechanism will nowi'be-Iles'cri-bed,-- I

The control of the length of the feed-step, just referred '-to-,- isexercised :by the inclinometer (Figs. 12, 13 and14). "An-important'member 0f the inclinometer' is the double cam surface. 56+58 which 'issecured to a supportw196-risingfrom ashaft 198 suitably journaled-ondelicate bearinggpoints in theinolinometer casing 52. --1 Depending fromthe shaft is a pendulum :weight" 200. Simcathe shaft- -198 is 'atransverse shaft, paralleltothe drum shaftf22 and cam -jshaft 150; thependulum weight-acts' to retain-the double tam. 56%58 vertical no matterwhat the fore-and-aftiobliquity of-the-tank may be. Theifeel'er 54i shou sed in--a vertical sleeve. 55 through'whioh it is moved to bear onthe surface of the inclinometer camtsee Figs. 13 and 14); An=adjustablespool202, threaded =on its upper end, is engaged by a horizontali'pi-nprojecting from the. free end of a'crank arm 204 fixed' 'on the outerend ofa horizontal rock-shaft-206 journaled in the sidef'rame 10 andtheinterior-bracket see Fig. 2). A second crank arm20 8 is fixecl'on' therock-shaft, fro'mthe end of which depends a'housing which receives theuppabthreaded-end of a -rod 210 (Fig. 4). 'l hisa'od is' pbovide'd with;a fixed-washer at its lowei end for supporting a coiled spring 212which, in -turn,' support s a sleeve 214 loose'on the rod! Abovefl-thesleeve the rod 210 "carries a fixed collar 216 forming an abutment forthe sleeve 214.; The sleeve is carried by theforked forward "end of thehorizontal arm 218-of a bell-crank pivoted on a shaft-220 (Fig. 4),bel0w the shaft 176 and similarly-mounted. The vertical arm 222 of thebell-cranl "'carries aroll 224 at its lower end which is engagedby'a campath 226 formed in the'outer face of the cam disk 172. Thevert-icalposition of the collar 216 is such that this cam path, throughthe connections just described, normally maintains the feeler 54 in aposition of clearance relative-to the center of the inclinometercan1*'56'58 at all times. This cam will be termed, forcom'enience, thefeeler cam. If the tank is travelling on level ground the feeler will bein central position, as shown by Fig. 14, and the downward movement ofthe bell-crank arm 218 will merely cause the feeler to engage the camand then compress 'thespring 212, but if the tank is tilted,fore-and-aft, then the first part of the throw of the feeler cam willact to lower the feeler until it contacts with one or the other of thecam surfaces 56 or 58 which is then beneath it. Such a movement of thefeeler carries the crank arm 208 downward with the following result.

Extending rearwardly from the hub 209, of the crank arm 208, is a leverarm 228 to the rear end of which is pivoted a depending'link 230 having"a roll 232 at its lower end which lies in front of a plane surface 233at the forward side of a shoe 234 which forms the terminal portion ofthe vertical bell-crank arm 180. Thus as the lever 228 is raised, by alowering of the feeler 54, the roll 232 rides up the shoe 234, and viceversa. Pivoted on the shaft 220 is a depending lever 236 ('see Figs. 4and 4) having a roll 238 at its lower end which is engaged by the feedcam 174. This lever 236 lies in the vertical plane of the bellcrank arm180 and is provided with a plane surface 240 opposite the shoe 234. Whenthe feed cam throws the lever 236 to the left, Fig. 4, it transmits itsmovement in varying degree to the belLcrank arm 180 through theinterposed roll 232 whatever may be the vertical position of this rollon the shoe 234 due to the elevation or depression of the. inclinometerfeeler 54.

A brake is employed to hold the map- !drum from movement during "thetime that it is not under control of the feed-point 40 and this brakemechanism will be explained before detailing the movements of themechanisms just described in making a feed-step. The brake comprises twoshoes 242 (Figs. 1 and 2) at the ends of arms extending rearwardlyfrom-a. brake frame 244 carried by a sleeve fixed on a transverse shaft246 that is journaled in the forward brackets 36 and 38 somewhat belowthe scriber shaft 34. The shaft 246 carries a second sleeve, at itsright-hand end, from which depends an arm 248 pivotally connected to theforward end of a yielding link 250, the rear end of which is pivotallyconnected to a cam lever 252 between its fulcrum pin 156 in the frameand its cam roll 254 at its lower end (see Fig. The roll 254 is engagedby a cam path 256 formed in the outer surface of the cam disk 152. Thebrake cam 256 is designed to periodically draw the link 250 to the rearand, by thus rocking the shaft 246 in a counter-clockwise direction,raise the brake shoes 242 into contact with the map on the drum 20. Theyielding link 250 is of common construction as clearly illustrated inFig. 3. After the brake shoes have been seated any excess throw of thecam is taken up by the sleeve 258 sliding rearwardly on the rod 260 andcompressing the spring 262 coiled thereon. The spring is confined inplace'by a nut 264 on the rear end of rod 260 having a flat side bearingon the under face of the link 250. The length of the link, to vary thebrake pressure, may be adjusted by any usual connection for thispurpose, shown at 264.

A hand lever 266 extends upwardly from the sleeve from which the arm 248depends, and by pressing this lever inward the brake may be heldreleased during adjustment of the map-drum on its shaft. The act ofwithdrawing the scriber 30 automatically releases the brake, and holdsit released until the scriber is returned to its operating position, dueto the provision of 'a cam 268, fixed on the scriber shaft just in frontof the hand lever 266, which engages'said lever and moves it clockwisewhen the scriberholder is moved counter-clockwise. This automaticrelease of the brake-is employed when it is desired to remove themap-drum from the instrument.

Having explained the mechanisms for imparting to the feed-point itsfour-motion travel and for holding the map drum in position during theperiods between each feed stroke, the sequence of operation of theseparts will now be described during the ad vance of the map through onefeed-step.

It will be assumed that the feed-point 40 is in its lower position,disengaged from the map, and at the beginning of its feed stroke, asillustrated in Figs. 4, 5 and 6. Rotation of the cam shaft 150 in thedirection of the arrows, from the position shown in these figures, willfirst cause the feeler cam 226 to move the cam roll 224 to the left, inFig. 4, by reason of the engagementtherewith of the cam-rise a shownjust above the roll 224 in that figure. This turns the bell-crank arm218 in a clockwise direction and, assuming that the tank is travellingon level ground with the feeler 54 at mid-point above its cam 56-58, thedownward movement imparted to the arm 208 will close this feelerclearance, the coiled spring 212 absorbing the excess of cam throw inthis position of the feeler or in any other posit-ion due to fore andaft tip of the tank. No movement of consequence being imparted to thearm 208, consequently the arm 228 and depending link 230 remain insubstantially the positions shown in Fig. 4, with the roll 232 still atthe lower end of the shoe 234.

While the feeler cam is rotating through the angle just described thefeed cam 174 also is being rotated and after the feeler clearance hasbeen closed the slight camrise (1 becomes effective to move the cam roll238 to the left, in Fig. 4, and impart a slight movement in a clockwisedirection to the bell-crank arm 180 by pressure thereon through the roll232. The purpose of this is to close down all clearance and loosenessthrough the parts, particularly between the parts 138 and 190 (Fig. 6)when all back-lash to the feed-point is taken up. It is thus apparentthat absolute accuracy of every feed step is secured. The subsequenttravel of the roll 224 in the feeler cam, after passing cam rise a, isthrough a dwell b of sufficient length to maintain the outward positionnow assumed by the roll 232 during the following operations. After theclearances have been closed there is a short dwell b on the feed cam andwhile the roll 238 is traversing this sector the roll 162 of the liftingcam 154 has reached the cam fall b which moves this roll to the left, inFig. 5, throws the bell-crank lever arm 160 upward and thus raises thegimbal-ring frame 112 which causes the feed-point 40 to enter the map onthe drum 20. The release of the brake shoes 242 by a fall of cam 256immediately follows. The cam rise 0 of the feed cam is now traversed bythe roll 238 thus continuing the movement of the leverarm 236 to theleft, in Fig. 54,-and through .movement'of the bell-crank-180- 182depresses the feed-arm actuatoflring 190 which, it will be remembered,is now in contact with the .feed armhook 138. During this time .thefeed-point is held in the map by a dwell c of the lifting cam 154. Thedepression of the actuator-ring 1'90 turns the forward end of tl e feedarm 136 downward and causes its fee hook 134' to move to the left, inFig. 6, which forces the slide. 128 to the left and consequently tiltsthe feed-point holder toward the rear within the forked end 126 of theshaft 44 and rotates the map drum in the direction of the arrow-shown-onthe drum in Fig...6..-.At:-the completion of the feed strokethe'liftingcam' roll encounters the cam rise d which moves the cam roll162 to the right; in Fig. 5, and-effects a disengagement of thefeed-point from the map. The feed cam .roll '238 is simultaneouslytravelling the .dwelld of its cam, but upon the feed-point becomingdisengaged the roll 238 encounters a cam fall e which causes the roll toreturn to,its position as shown in Fig. 4, the bell-crank180182 beingrotated in a counter-clockwise direction at this time. The spring 191causes the bell-crank arm 180 to follow the movement of the lever 236 tothe left and finally lifts the actuator ring 190 clear of the feed hook138. Almost simultaneously .with this last operation the cam fall infeeler cam-2'26 restores the feeler mechanism to a position of clearancerelative to the inclinometervcam. This constitutes one cam cycle.

The brake cam 256 is so designed that before the feed-point 40 iswithdrawn from the map by the rise (1 of the lifting cam 1.54 oncompletion of the feed stroke, its roll 254 is moved to the right inFig. 3, which causes the brake sho es to-rise and yieldingly engage themap to hold the drum from movement until it is'again under control ofthe feed-point. During the brief period that the feed-point isoperating, the brake shoes are held ininoperative position by a shortdwellc of the brake cam 256, but during the greater part of the cyclethe brake is on by reason of the. travel of cam roll 254 through thelo'ngilwell (i 1 If the tank is travelling'on a grade, for exampleup-hill, then the entire instrument will be tilted backwardrelative to.the inclinometer cam, and the feeler 54 will be brought toa positionabove the curved portion 56. of the cam. Consequently when the cam risea of the feeler cam 226 engages the ro-ll 238 the. downward movement ofthe bellcrank arm 21.8 will continueto' lower the feeler until itengages, or feels. the portion of the cam 56 just below it, and aftersuch engagement .has been' effected the excess throw of the cam'will beabsorbed by the coilspring 212 :as before Thisdownward movement ofxthefeeler 54 causes a similar downward movement of the crank arm '208 and aconsequent upward movement of t-he link 230; JIhe roll 232 is,therefore, caused to travel up the shoe". 234, the amo'unt'of suchmovement being dependent upon. the inclination of thetank,-i.-e.-"the:degree, .or

per cent of the grade upwhich the tank is travelling.

It will be observed; see Fig. 4, thatzthe plane surface 24-0 of the camlever.-236'ex tends at an angle-to the opposedplane surface 233 of theshoe 234 before the feed stroke is started. =The diameter of the roll232 is less than the distancebetween these two surfaces atthe lower endsthereof, therefore, as the roll is drawn upward on the shoe 234 undercontrol'of the inclinometer it fits more and more snugly into theintervening space, but=neverke1iactly=.: Since the throw of the cam risea" of the feed cam 174 is constant the resulting-effect of thisconstructionis to cause the vertical-bell-crank arm 180 to-be movedfurtherand-further to the left, in Fig. 4, during't'he time of-closingthe clearances, dependent upon the vertical position of the roll 232between the surfaces 233 and 240. In any position of the roll 232 thefirst por tion of the-throw from the cam rise a is ineffective to movethe bell crankarm 180 be cause this portion of the cam rise merelycloses the clearance between the surfaces 233 and 240. The completethrow will close all clearances to the' feed-point as hereinbeforereferred to. As the roll 232 is raised on the shoe 234 this clearancebetween the surfaces 233 and 240 becomes less and less and the cam risea becomes increasingly effective to move the bell-crank arm 180. Theobliquity of the angle at which the plane surface 240 lies with relationto the surface of the shoe 234 is so proportioned,.with relation to theupward movement imparted to the roll 232 by variations in the positionof the feeler 54 as it feels different portions of its cam 5658. thatthis preliminary movement of the bell-crank arm 180 shortens the feedstroke in the exact percentage required for delineating on the map anair-line distance when the actual travel or rolling contact on theground is a greater distance. With this construction the shortening ofthe feed stroke .is always by altering its starting point, and

the timing is such that the feed-point is turned through the small anglerequired to effect this compensation before the lifting cam 154 operatesto cause an engagement of the feed point with the map. The completion,or finish point, of the stroke of the feedpoint is always the same; Fig;4 illustrates the position of the parts at the completion of a feedstroke. It will be observed that, due to the different centers aboutwhich the levers 180 and 236 move, the two surfaces 233 and'240 areparallel when the cam roll 238 enters the dwell d of the feed cam and,therefore, each feed stroke, no matter what its length has been, ends atthe same point with the roll 232 confined between the two levers. 1

Returning now to the inclinometer 60, its casing 52 is provided withlugs 270 by which it is removably secured to the side frame 10, theloose pin and spool connection 202-204 being so made for this purpose.The casing 52 may be opened from its inner side. This opening is closedby an 'inner'plate 272 (Figs. 13 and 14) which has formed thereon thefeeler housing 55 and one bearing of the pendulum fulcrum 198. Outsidethe plate 272 is the .cover plate 274, the 'whole being securedtogetherby a'peripheral series of screws, as shown, forming fluidtight joints.

' In order to damp the oscillations of the pendulum, although stillallowing action of reasonable alacrity when the casing is tilted, thecasing is filled with a fluid which should be noncongealing. for examplekerosene. The fluid is introduced through an opening at the top of-thecasing, a closure 276 being first removed. The fluid fills the pendulumchamber 278, the feeler cam chamber 280 and the expansion chamber 282 tothe level shown by the dash line. In filling, the fluid is pouredthrough a filling port 284, which is opened when the cap 276 is removed,into a chamber 286 within a casting 288 seated in the upper sector ofthe pendulum chamber, and then fills all the open spaces within thecasing by flowing through'the ports 290 in the inner plate 272. At theupper side of the casting 288 a groove 292 is cut that forms a bleederpassage for the escape of air during the filling operation. When the cap276 is replaced, after filling, the stem 294 thereof screws into thefilling port 284 and closes communication between the bleeder passageand the expansion chamber 282. The stem is provided with a central port296--forming a communicating passage between the pendulum' and expansionchambers. The pendulum weight 200 is of slightly less crosssectionalarea than that of its chamber 278 thus providi g by-passes for the fluidto flow from one side to the other of the weight whenever a tilting ofthe odograph requires such exchange. As the liquid escapes by the sidesof the pendulum to the opposite chamher, the action of the pendulum isdamped not only by the restricted area through which the liquid escapesbut also by the skin friction of the liquid travelling past thependulum, thereby producing great sensitiveness to the steady pull ofgravity and great resistance to all forces tending to'set uposcillations. A cock 298 is tapped into the casing at its lowest pointto facilitate drawing off the contained fluid when necessary.

A well known peculiarity of balanced gyroscopes is that a change intheir position is effected more easily by a steady, sustained pressurethan by. a sharp, quick blow, in

fact the latter is substantially ineffective to alter the gyroscopesposition. An impor-. tant feature of the present invention resides inunfailingly maintaining the gyroscope in its set position sinceotherwise the fundamental base line direction, to which the compassbearings and selected direction of feed are referred, would be lost, andthe scriber would trace an untrue course on the map. In order to preventa sustained drag on the gyroscope from the operationof the feedpoint thecam shaft 150'is operated inter' mittently, driving quickly through onerevolution and then remaining at rest until the tank has traveledsubstantially the whole of the unit distance to be measured and markedonthe map at eachfeed-step of the feedpoint. In this way the resistanceoffered by the successive feeds .is transmitted to the gyroscope as asuccession of sharp blows and any tendency of the feed to alter theoriginal base-line direction is thus overcome. The mechanism for ac-.complishing this, although not essential, is mounted within the gear boxand will now be explained.

The flexible drive 62 couples into a foreand-aft shaft 299, journaled ina sleeve 1300, and provided with a worm 300 at its rear end (Figs' 15and 16) which drives the reduction gearing 64. This gearing comprises aworm-wheel 301 on a cross shaft 302 journaled in a bearing carried bythe outer casing wall; a small pinion 303 on the inner end of shaft 302;a large gear 304 on a stub shaft 305 journaled in a hearing 1305 whichextends between the gear box walls and supports the sleeve 1300, meshingwith the pinion 303; a smaller gear 306 outside the gear 304; and alarge gear 307 carried on a lower cross shaft 308 journaled in the twogear box walls, meshing with the gear 306. The shaft 308 also carries adisk provided with a tappet cam 309 (Fig. 20) which periodically (asherein designed ninety-six times for each mile traveled by the tank)engages and depresses a roll 310 at the forward end of a centrallypivoted lever 311 the rear end of which pro vides a hunter 312 forengaging and lifting a rod 313 guided vertically in a housing 314: onthe rear wall of the gear box.

Before describing the effect of lifting the rod 313, it will beexplained that the cam shaft 150 is coupled to a shaft 315 (Figs. 19 and20) in axial alignment therewith, and journaled in a bearing at theupper end of the gear box 70. This shaft 315 carries a sleeve on whichis mounted the loose member 316 of a one revolution clutch and aconnected gear 317 (F ig."16) which may mesh directly with a gear 318 onthe worm-wheel shaft 302, thus constantly rotating the clutch member 316while the tank is moving. For convenience in driving from either a rightor a left transmission two intermediate gears 319 and 320 are adjustablymounted on the outer casing wall (see Figs; 3 and 16) in such mannerthat the gear 320 'may be disconnected at will'and' the gear 319enmeshedwith both gears 317 and318. The fast member .of the clutch is keyed tothe shaft" 315 and comprises a frame 321 (Figs. 19 and 20) having alever 322 pivoted thereon:whichcarries a roll 323 at one end. The roll323'is normally held by a spring 324"in position to be engaged by one orthe other of two coupling shoulders 325 in which 'eventthe shaft 315 isdriven, but when the roll engages a shelf 326 on the vertical arm 327of'a bell-crank pivoted at 328 on the casing (see Fig. 19) it is heldinside the path of movement of the coupling shoulders 325 and rotationof the shaft 315 ceases Returning now'to the bunter'rod 313, its upwardmovement lifts the horizontal arm 329 of thebell-crank pivoted at 328thus tipping the=vertical arm 327 to the left, in Fig. 19, andpermitting the spring 324; to

throw the roll 323 into the path of the ro-- tating coupling shoulders.The bell-crank is immediately restored to its position shown in Fig. 19by reason of the upper pivotally connected end 3300f the hunter rodbeing cammed off the bell-crank by a fixed pin 331 and the tension of acoiled spring 332 which draws the vertical arm forward against a stop333. The roll 323 engages the upper end of the-arm 327 after onerevolution of the shaft'and is cammed thereby into position to seatagainst the shelf 326, stopping rotation of the shaft 315. To preventrebound, due to inertia of the parts, the cam shaft 150 is drivenagainst the continual pressure of a friction brake 151 (Fig. 1) pivotedon a pin 153 and held in contact with the peripheral surface of cam disk152 by a suitably connected torsion spring 155.

It'will be observed from the relative positions of the parts in Figs. 16and 20 that 1,727,a-eo

a complete revolution of shaft 315 takes place during the travel of thetappet cam 309 through a very small are so that the mechanism insures aquick, periodic feed,

stroke by the feed-point 40, the cam shaft 150 being idle duringsubstantially all of the linear travel of the tank that is transcribedon the map by the scriber 30 when the drum finally is moved by thefeed-point.

The gearcasing is provided with a filling opening 334 through which oilis introduced to maintain the gearing in an oil bath, the level of theoil being just below the shaft 299 which couples to the flexible drive62. The pivoted end 330 of the hunter has a horizontal arm 1330 (Fig.19) normally held in the position shown by a spring 1331 and this springlowers the hunter and restores the part 330 to a position beneath thebell-crank for successive upward 'move ments to throw in the cam shaftclutch.

' The-map drum 20, as the illustrated odograph is designed, mounts asmall map representinga terrain about two miles in width by five milesin'length on the usual scale of war maps. This-map. having an area often square miles which is deemed suflicient by army strategists for thefield of operation, may be obtained by removing or tracing a small mapof this approximate area from a larger war map. Examples of how this isdone will now be explained.

Referring to Fig. 17 it is preferable, for reasons which presently willappear, to remove or trace from the large map M a portion m which whileincluding the starting point and objective, lies with its longitudinalaxis n parallel to north on the map M. If the starting point andobiective are so located relatively to each other that this relation ofthe map axis and north cannot be obtained, as for example in the case ofthe small map m then the angle by which the map axis 12, deviates fromnorth on the map M must be measured and compensated for when such asmall map as m is mounted on the map drum.

It is obvious if map m is wound evenly on the map drum. the dial 340 isset to zero as in Figs. 6 and 7. and the tank is then pointed truenorth, that so long as the tank travels north the path of the feed-pointwill be in a north and south plane and the scriber will mark a pathparallel to the map axis at each feed step, as is correct. The

odograph may be located in any position but always with the map drumshaft lying crosswise of the tank. Should the direction of advance bealtered to north-east then the instrument turns with the tank about thegyroscope which maintains its fixed north and south base-line direction.The next feed step of the feed-point. which still is held in its northand south plane through control by the gyroscope, will not only rotatethe map drum butwill simultaneously slide it to the left, in Fig. 1,causing the scriber to mark the resultant of these two components, i. e.a path that is north-east relative to the map axis. Should the course ofthe tank be due west then the feed-point would move in a plane east onthe map, merely sliding the drum on its shaft and the scriber would marka westerly course.

And so on for every travel unit covered by the tank the scriber marks apath on the map, in the true direction of advance, and proportionate inextent to the horizontal distance travelled by the tank between eachperiodic feed step of the feed-point. The tank commander is thus enabledto tell, at any instant, exactly his position in the advance toward hisobjective and be guided accordingly.

If a small map similar to m is wound on the drum with the odograph inthe same position in the tank as just described for mounting the smallmap m, then on sighting the tank true north there will be a deviationof"north on the map from true north. In Fig. 17- this is shown, by wayof example, as 22 With the dial 340 again set to zero as before, thescribe f would mark a path north-north-west when the tank was in realitytravelling north. Under such a condition the deviation of north on themap from true north, or any other base-line direction that may beselected, must be compensated for. This may be accomplished by rotatingthe shaft 44, which supports the feed-point, in such a direction as toset the plane in which the feed-point moves at the same angle to thegyro-rotor shaft that north. on the map varies from true northremembering, however, that since the path marked by the scriber extendsin the opposite direction to the-advance of the feedpoint, the anglethrough which the feedpoint is turned, when rotating the shaft 44 fromright to left, in Fig 7, must be the difference between the angle ofdeviation and 360. When rotating the shaft 44 from left to right then itis turned through the angle of deviation only. The means through wliichthe direction in which the feed-point moves may be varied from thebase-line direction as determined by the gyroscope, 1. e. a. variationfrom the set-up as shown by the drawings, will now be explained.

cferring to Fig. 6 the stand 142 which supports the shaft 44 is providedwith a cross-slot with external threads 336 gust above it, and with acircular flange 337 at its upper end. The stand is also bored axially toreceive the shaft 44, this bore formingan enlargement 338 just above thegyro pintle 46 and also being counter-bored at'its upper end to receivea sleeve 339 fast on the shaft 44 which has a flange 340 overlylng andnesting within the flange 337. The lower end of shaft 44 has a circulargroove that is embraced by the inwardly projecting tongues 341 (Fig. 9)of two semi-circular plates 342 located beneath a locknut 343 receivedon the threads 336. The lower face of the locknut is recessed, asillustrated, to protect these two plates and hold their tongues 341above a head 344 formed by the groove. l Vith this construction, whenthe lock-nut 343 is screwed down the tongues 341 bear on the shaft head344 and hold the shaft from rotation within the stand 142 by bringingthe twoflanges 337 and 340 into close frictional contact. On looseningthe lock-nut the pressure is relieved and the shaft 44 may be rotatedfreely within the stand, at the same time turning its flange 340angularly relative to the fiked flange 337 beneath it- These two flangesareebeveled at their edges and are marked with graduations indicatingdegrees (Fig. 7); T.

It will be understood then, that in order to vary the angle of the planein which the feed-point moves, i. e. shift the feed-point holder 130angularly from its location as shown in Figs. 6 and 7, it is merelynecessary to loosen the lock-nut 343 and then .turn the shaft 44 thedesired'number of degrees, after which, by tightening the lock-nut, thefeedpoint will be securely held in its new plane of travel.

The advantage of providing a circular feed arm actuator 190 will now beapparent, since in this form it is effective to depress the feed yoke136 for any angular position to which the-feed-point holder may beadjusted. Furthermore the circular form of the feed arm actuator permitsit to turn about the feedpoint holder and gyroscope, whenever the tankchanges its direction of advance, and yet continually maintain itsoperative relation to the feed arm hook 138. The importance of theclearance between the actuator and feed arm will now be understood sincewithout this clearance the continual turning of the instrument past andin contact with the feed arm hook 138 would exert a drag on thegyroscope that would eventually affect its predetermined base-linedirection and destroy its value as a directional constant. It is highlyimportant that precessing of the gyroscope 'be prevented.

In adjusting the feed-point to compensate for the condition hereinbeforementioned when the small map m (Fig. 17) is wound on the drum, theflange 340 would be rotated from left to right, in Fig. 7, until 22 asmarked on said flange registers with zero on the flange 337. A sighthole 345 (Fig. 2) is provided in the brake frame 244 which enables theoperator to see the forward portions of the two flanges from above.\Vithin the sight hole is a V-shaped sight 346 and interposed betweenthe sight and zero on dial 337, conveniently projecting forwardly fromthe

